This invention relates to sealing of thermoplastic material and more particularly to a process for sealing the gathered end of a thermoplastic bag so as to obtain an airtight seal.
A common method of sealing the open end of a thermoplastic container requires that opposite sides of the open mouth be brought together and that sufficient heat be applied to the thermoplastic material to fuse the two sides together. This necessarily results in a rather wide closure extending the width of the package which, while suitable for packaging some products, is equally unsuitable for others. For example, when packaging primal meat cuts, it is preferred that the bag including the sealed area, closely conform to the product. Conventional heat sealing, therefor, produces seals that lie some distance from the end of the product and are relatively straight loose fitting seals.
Another method of closing bags and one that sets the sealed area to more closely conform to the product involves the application of a formable metal band about the gathered end of the bag. A band or clip can be applied to the gathered end of the bag in close proximity to the bagged product. With the development of clip applying devices and suitable clips, it is possible to quickly obtain reliable seals. Several problems exist in connection with such sealing, however. The most serious problem is fracture of the container in the clipping process.
Attempts to overcome this problem have been made in the prior art. One such attempt is described in U.S. Pat. No. 3,111,794 to Spolsino. The process described within this patent is directed to a process of fusing a bag end into a solid unitary mass. Another such technique is described in U.S. Pat. No. 3,358,905 wherein a thermoplastic ring is placed around a skein type bag ending and the ending and skein fused into a solidified mass.
While these prior art techniques form satisfactory container closures the time consumed for forming such closures is inordinately long.